/** \file autoload.cpp

The classes responsible for autoloading functions and completions.
*/

#include "config.h"
#include "autoload.h"
#include "wutil.h"
#include "common.h"
#include "signal.h"
#include "env.h"
#include "exec.h"
#include <assert.h>
#include <algorithm>

/* The time before we'll recheck an autoloaded file */
static const int kAutoloadStalenessInterval = 15;

file_access_attempt_t access_file(const wcstring &path, int mode)
{
    //printf("Touch %ls\n", path.c_str());
    file_access_attempt_t result = {};
    struct stat statbuf;
    if (wstat(path, &statbuf))
    {
        result.error = errno;
    }
    else
    {
        result.mod_time = statbuf.st_mtime;
        if (waccess(path, mode))
        {
            result.error = errno;
        }
        else
        {
            result.accessible = true;
        }
    }

    // Note that we record the last checked time after the call, on the assumption that in a slow filesystem, the lag comes before the kernel check, not after.
    result.stale = false;
    result.last_checked = time(NULL);
    return result;
}

autoload_t::autoload_t(const wcstring &env_var_name_var, const builtin_script_t * const scripts, size_t script_count) :
    lock(),
    env_var_name(env_var_name_var),
    builtin_scripts(scripts),
    builtin_script_count(script_count)
{
    pthread_mutex_init(&lock, NULL);
}

autoload_t::~autoload_t()
{
    pthread_mutex_destroy(&lock);
}

void autoload_t::node_was_evicted(autoload_function_t *node)
{
    // This should only ever happen on the main thread
    ASSERT_IS_MAIN_THREAD();

    // Tell ourselves that the command was removed if it was loaded
    if (! node->is_loaded)
        this->command_removed(node->key);
    delete node;
}

int autoload_t::unload(const wcstring &cmd)
{
    return this->evict_node(cmd);
}

int autoload_t::load(const wcstring &cmd, bool reload)
{
    int res;
    CHECK_BLOCK(0);
    ASSERT_IS_MAIN_THREAD();

    env_var_t path_var = env_get_string(env_var_name);

    /*
      Do we know where to look?
    */
    if (path_var.empty())
        return 0;

    /* Check if the lookup path has changed. If so, drop all loaded files. path_var may only be inspected on the main thread. */
    if (path_var != this->last_path)
    {
        this->last_path = path_var;
        this->last_path_tokenized.clear();
        tokenize_variable_array(this->last_path, this->last_path_tokenized);

        scoped_lock locker(lock);
        this->evict_all_nodes();
    }

    /* Mark that we're loading this. Hang onto the iterator for fast erasing later. Note that std::set has guarantees about not invalidating iterators, so this is safe to do across the callouts below.  */
    typedef std::set<wcstring>::iterator set_iterator_t;
    std::pair<set_iterator_t, bool> insert_result = is_loading_set.insert(cmd);
    set_iterator_t where = insert_result.first;
    bool inserted = insert_result.second;

    /** Warn and fail on infinite recursion. It's OK to do this because this function is only called on the main thread. */
    if (! inserted)
    {
        /* We failed to insert */
        debug(0,
              _(L"Could not autoload item '%ls', it is already being autoloaded. "
                L"This is a circular dependency in the autoloading scripts, please remove it."),
              cmd.c_str());
        return 1;
    }
    /* Try loading it */
    res = this->locate_file_and_maybe_load_it(cmd, true, reload, this->last_path_tokenized);

    /* Clean up */
    is_loading_set.erase(where);

    return res;
}

bool autoload_t::can_load(const wcstring &cmd, const env_vars_snapshot_t &vars)
{
    const env_var_t path_var = vars.get(env_var_name);
    if (path_var.missing_or_empty())
        return false;

    std::vector<wcstring> path_list;
    tokenize_variable_array(path_var, path_list);
    return this->locate_file_and_maybe_load_it(cmd, false, false, path_list);
}

static bool script_name_precedes_script_name(const builtin_script_t &script1, const builtin_script_t &script2)
{
    return wcscmp(script1.name, script2.name) < 0;
}

void autoload_t::unload_all(void)
{
    scoped_lock locker(lock);
    this->evict_all_nodes();
}

/** Check whether the given command is loaded. */
bool autoload_t::has_tried_loading(const wcstring &cmd)
{
    scoped_lock locker(lock);
    autoload_function_t * func = this->get_node(cmd);
    return func != NULL;
}

static bool is_stale(const autoload_function_t *func)
{
    /** Return whether this function is stale. Internalized functions can never be stale. */
    return ! func->is_internalized && time(NULL) - func->access.last_checked > kAutoloadStalenessInterval;
}

autoload_function_t *autoload_t::get_autoloaded_function_with_creation(const wcstring &cmd, bool allow_eviction)
{
    ASSERT_IS_LOCKED(lock);
    autoload_function_t *func = this->get_node(cmd);
    if (! func)
    {
        func = new autoload_function_t(cmd);
        if (allow_eviction)
        {
            this->add_node(func);
        }
        else
        {
            this->add_node_without_eviction(func);
        }
    }
    return func;
}

/**
   This internal helper function does all the real work. By using two
   functions, the internal function can return on various places in
   the code, and the caller can take care of various cleanup work.

     cmd: the command name ('grep')
     really_load: whether to actually parse it as a function, or just check it it exists
     reload: whether to reload it if it's already loaded
     path_list: the set of paths to check

     Result: if really_load is true, returns whether the function was loaded. Otherwise returns whether the function existed.
*/
bool autoload_t::locate_file_and_maybe_load_it(const wcstring &cmd, bool really_load, bool reload, const wcstring_list_t &path_list)
{
    /* Note that we are NOT locked in this function! */
    bool reloaded = 0;

    /* Try using a cached function. If we really want the function to be loaded, require that it be really loaded. If we're not reloading, allow stale functions. */
    {
        bool allow_stale_functions = ! reload;

        /* Take a lock */
        scoped_lock locker(lock);

        /* Get the function */
        autoload_function_t * func = this->get_node(cmd);

        /* Determine if we can use this cached function */
        bool use_cached;
        if (! func)
        {
            /* Can't use a function that doesn't exist */
            use_cached = false;
        }
        else if (really_load && ! func->is_placeholder && ! func->is_loaded)
        {
            /* Can't use an unloaded function */
            use_cached = false;
        }
        else if (! allow_stale_functions && is_stale(func))
        {
            /* Can't use a stale function */
            use_cached = false;
        }
        else
        {
            /* I guess we can use it */
            use_cached = true;
        }

        /* If we can use this function, return whether we were able to access it */
        if (use_cached)
        {
            assert(func != NULL);
            return func->is_internalized || func->access.accessible;
        }
    }
    /* The source of the script will end up here */
    wcstring script_source;
    bool has_script_source = false;

    /* Whether we found an accessible file */
    bool found_file = false;

    /* Look for built-in scripts via a binary search */
    const builtin_script_t *matching_builtin_script = NULL;
    if (builtin_script_count > 0)
    {
        const builtin_script_t test_script = {cmd.c_str(), NULL};
        const builtin_script_t *array_end = builtin_scripts + builtin_script_count;
        const builtin_script_t *found = std::lower_bound(builtin_scripts, array_end, test_script, script_name_precedes_script_name);
        if (found != array_end && ! wcscmp(found->name, test_script.name))
        {
            /* We found it */
            matching_builtin_script = found;
        }
    }
    if (matching_builtin_script)
    {
        has_script_source = true;
        script_source = str2wcstring(matching_builtin_script->def);

        /* Make a node representing this function */
        scoped_lock locker(lock);
        autoload_function_t *func = this->get_autoloaded_function_with_creation(cmd, really_load);

        /* This function is internalized */
        func->is_internalized = true;

        /* It's a fiction to say the script is loaded at this point, but we're definitely going to load it down below. */
        if (really_load) func->is_loaded = true;
    }

    if (! has_script_source)
    {
        /* Iterate over path searching for suitable completion files */
        for (size_t i=0; i<path_list.size(); i++)
        {
            wcstring next = path_list.at(i);
            wcstring path = next + L"/" + cmd + L".fish";

            const file_access_attempt_t access = access_file(path, R_OK);
            if (access.accessible)
            {
                /* Found it! */
                found_file = true;

                /* Now we're actually going to take the lock. */
                scoped_lock locker(lock);
                autoload_function_t *func = this->get_node(cmd);

                /* Generate the source if we need to load it */
                bool need_to_load_function = really_load && (func == NULL || func->access.mod_time != access.mod_time || ! func->is_loaded);
                if (need_to_load_function)
                {

                    /* Generate the script source */
                    wcstring esc = escape_string(path, 1);
                    script_source = L"source " + esc;
                    has_script_source = true;

                    /* Remove any loaded command because we are going to reload it. Note that this will deadlock if command_removed calls back into us. */
                    if (func && func->is_loaded)
                    {
                        command_removed(cmd);
                        func->is_placeholder = false;
                    }

                    /* Mark that we're reloading it */
                    reloaded = true;
                }

                /* Create the function if we haven't yet. This does not load it. Do not trigger eviction unless we are actually loading, because we don't want to evict off of the main thread. */
                if (! func)
                {
                    func = get_autoloaded_function_with_creation(cmd, really_load);
                }

                /* It's a fiction to say the script is loaded at this point, but we're definitely going to load it down below. */
                if (need_to_load_function) func->is_loaded = true;

                /* Unconditionally record our access time */
                func->access = access;

                break;
            }
        }

        /*
          If no file or builtin script was found we insert a placeholder function.
          Later we only research if the current time is at least five seconds later.
          This way, the files won't be searched over and over again.
        */
        if (! found_file && ! has_script_source)
        {
            scoped_lock locker(lock);
            /* Generate a placeholder */
            autoload_function_t *func = this->get_node(cmd);
            if (! func)
            {
                func = new autoload_function_t(cmd);
                func->is_placeholder = true;
                if (really_load)
                {
                    this->add_node(func);
                }
                else
                {
                    this->add_node_without_eviction(func);
                }
            }
            func->access.last_checked = time(NULL);
        }
    }

    /* If we have a script, either built-in or a file source, then run it */
    if (really_load && has_script_source)
    {
        if (exec_subshell(script_source, false /* do not apply exit status */) == -1)
        {
            /* Do nothing on failure */
        }

    }

    if (really_load)
    {
        return reloaded;
    }
    else
    {
        return found_file || has_script_source;
    }
}
